The present invention relates generally to a building automation control system, and more specifically, but not exclusively, to use of a high dynamic range (HDR) sky map for predictive control.
This disclosure relates to a photometric device controlled wirelessly or directly by a microcontroller and/or a back-end computer system to control a building's automated daylighting fenestration system.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
It has been determined that the use of daylight harvesting (DH) to replace or supplement electric lighting in buildings can result in significant energy and demand savings as well as improve comfort and visual performance. For example, DH may be accomplished using lighting control systems that are able to dim or switch electric lighting in response to changing daylight availability. High performance fenestration systems are a necessary element of any successful daylighting design that aims to reduce lighting energy use. New fenestration technologies have been developed that aim at controlling the intensity of the incoming solar radiation, its interior distribution and its spectral composition, as well as thermal losses and gains. For best performance these fenestration systems often incorporate automated components such as, but not limited to, shades, Venetian blinds, interior/exterior fixed and adjustable louvers, electrochromic glazings, and optical components, such as, light redirecting devices, in order to respond to the dynamic nature of daylight and its component parts of direct sun, diffuse sky and exterior objects reflecting on to the fenestration. These controls are with respect to openings or portals in a building or wall envelope, such as for windows, doors, louvers, vents, wall panels, skylights, storefronts, curtain walls, and slope glazed systems.
Automated fenestration (AF) systems use a combination of photometers and computer algorithms to measure and predict real time sun and sky conditions in order to control how these systems modulate natural, daylight illumination in the interior spaces of buildings while preventing glare, heat-gain and brightness discomfort for the building's occupants. Current fenestration control systems, like SolarTrac by MechoShade, employ an array of exterior mounted radiometers and photometers to measure sky conditions and sky brightness' from a building's roof top as well as from specific façade orientations (e.g. north, east, south, west). The measured radiometric values from the roof are compared against published theoretical values for specific latitudes to determine if the sky condition is clear or overcast. When the sky is cloudy the shades are raised. When clear and sunny the system adjusts the shades of each fenestration orientation according to the solar geometry for that orientation and the desired depth of direct sun allowed to enter in to the space. The photometric values of sky brightness, measured vertically from discrete façade orientations, are compared against specified luminance levels to determine if shades need to be closed for control of visual and thermal comfort.
Unfortunately these systems require multiple radiometers and photometers, each capable of taking only very specific measurements (i.e. irradiation, luminance or illuminance) of only the global component of the sky (i.e. the diffuse sky and solar contribution are measured together). Without the ability to sample the sky directionally and discreetly clouds cannot be discerned from the clear sky component to determine such metrics as amount of cloud coverage, cloud size and brokenness of cloud coverage. These measurements are necessary for approximating and predicting if, when, and for how long the sun is or may be occluded by clouds. Without the latter capabilities, AF systems tend to either not react in time, or to overreact when control is or is not needed.
Additionally, the façade mounted photometers inability to separately measure the direct solar component and diffuse sky component at different facade orientations impedes their ability to control for glare and direct gain. The effects of these two components on visual glare and thermal gain are different, requiring each to be measured separately. Sun hitting a photometer at an angle to its receiving surface's orientation will cause a high photometric reading, but may not be a source of glare if the angle is such that the circumsolar region is out of the visual field of the occupants. In contrast, a relatively lower photometric reading of a bright, overcast sky in the visual field of building occupants may be high enough to be a source of visual discomfort.
Furthermore, the integration of photometers with fenestration systems is costly and complicated limiting its market share and the benefits associated with it.
What is needed is a system and method for measurement and accurate prediction of sky/weather influence on building systems that respond to sky-related environment changes.